How Erections Work

AskMen Science: We Took A Long, Hard Look At What Makes Your Manhood Tick

You probably don’t remember the first time that you got an erection. That’s because it almost certainly happened when you were an infant. Infant males start getting erections at an early age, as their nervous systems develop. Most will also play with themselves and may even engage in masturbation-type behavior. It’s all part of developmental discovery, and is considered completely normal and healthy.

Some parents, not knowing this, freak out and worry that their kids are becoming sexual at too early of an age. They may unintentionally shame their sons, which can lead them to have some toxic feelings about sex, masturbation, and their bodies.

While shaming boys for getting erections and playing with their penises is to be avoided, as boys get a little older, it’s important to establish boundaries in terms of where and when it’s appropriate to play with oneself — for example, no masturbating at the dinner table.

By adolescence, most boys become well aware that their dicks get hard and that stimulation feels good. It’s usually around puberty that most guys start masturbating to get off. It’s also around that time that spontaneous boners become a thing.

Many guys have traumatic memories of spontaneous boners happening at the most embarrassing times, like in class, on the bus, or hanging out at the swimming pool. It’s pretty much a universal experience. Spontaneous boners can be the result of random nervous system activity, and can also be due to unnoticed sexual arousal (i.e., horniness).

But while most guys have spent a lot of time thinking about their erections, they might not know much about how and why they happen — so I'm going to clear all that up for you.

Why Do Men Get Erections?

Many species of animals get erections. Humans belong to the order Primates, and all primates get erections. However, humans are one of the few species that don’t have bones in their penises (despite the fact that we call erections boners).

Erections have developed over evolutionary history as a really good sperm-depositing tool. They allow for sperm to be shot deep into the vagina, maximizing the likelihood of pregnancy occurring.

It just so happens that erections, being external, also allow for easy access for pleasurable stimulation, either on one’s own, or with a partner. Some people have gone so far as to suggest that there’s an evolutionary reason why humans’ hands perfectly reach the groin area.

What Causes Erections To Happen?

Erections can result simply from touching the penis, even if the brain doesn’t notice. This is due to a reflex loop near the bottom of the spine. Nerve endings in the penis sense touch, and the resulting signal is sent to the spine through a set of nerves. The signal gets noticed in the spine, and then another set of nerves carry that processed signal back to the penis. That processed signal leads to an erection.

This reflex reaction can happen without awareness, which is one of the reasons guys get what feel like surprise boners. If the brain does notice, though, it can exert some control. This ability to control erections varies across men and depends on several factors.

While erections can be purely reflexive, the main way in which they happen is through the experience of being turned on (i.e., sexually aroused). When a guy gets turned on, his brain sends signals to his penis to get hard. For this reason, the hardness of a guy’s dick is a pretty good barometer of how aroused he is.

Many things can lead a person to be turned on. For example, noticing someone sexually attractive, fantasizing, and watching porn usually elicit sexual arousal, and as a result, erections. Physical stimulation of the penis can also increase sexual arousal, and therefore erections.

What Is The Erection Mechanism?

Erections are the result of a complex process that primarily involves the body’s nervous system (your brain and nerves) and circulatory system (your heart and blood). To understand how erections work, you need to know some basics about both systems.

There are two parts to the nervous system that run throughout the body. The first is the somatic nervous system, which gives us conscious control over our skeletal muscles. So, for example, say you want to lift up an apple with your arm. You think about it and do it. You are able to consciously make your arm lift the apple. The somatic nervous system isn’t really involved in erections.

The other nervous system is the autonomic nervous system. It controls our internal organs, and affects things like heart rate, digestion, breathing, and reproduction. With exception of breathing, the autonomic nervous system isn’t normally something that we can consciously control unless we learn to. The autonomic nervous system plays a crucial role in erections.

There are two branches that make up the autonomic nervous system: the sympathetic branch and the parasympathetic branch.

The sympathetic branch is primarily responsible for our fight-or-flight response. When we’re faced with threat, either real or perceived, the sympathetic branch prepares us for action. It gets us ready to deal with the threat by fighting or running away, which ultimately will keep us safe.

Arousal of the sympathetic branch leads to things like increased heart rate and breathing rate, and dilation of our pupils. The fight-or-flight system responds to psychological or emotional threat in the same way. When the fight or flight system is activated, we feel fear, which is at the core of anxiety. People feel anxious in response to physical or psychological threat.

When we feel emotional arousal, it is the sympathetic branch of the autonomic system getting all fired up. In the context of sex, ejaculation is the result of sympathetic branch arousal. If sufficient arousal is achieved, you'll ejaculate semen.

The parasympathetic branch of the autonomic nervous system is active when we are safe and at rest. It is responsible for things like digestion. It’s also responsible for erections.

The parasympathetic branch and the sympathetic branch of the autonomic nervous system are complementary, so when one is more fired up, the other is usually less so. This makes sense. If you’re fighting off a saber-tooth tiger, you don’t want to be wasting energy digesting your wooly-mammoth burger or trying to get an erection. Ideally, we spend more of our time in the parasympathetic zone; being in a constant state of sympathetic arousal is hard on the body, and is associated with chronic stress.

Now for the circulatory system: Arteries are blood vessels that carry oxygenated blood from the lungs via the heart to feed the tissues of the body; veins are blood vessels that carry deoxygenated blood back to the lungs to be oxygenated.

The walls of the arteries are lined with smooth muscle tissue, which can contract to make the diameter of the arteries smaller, or relax to make the diameter larger. This process is essential for erections to happen.

So What Does This All Have To Do With Erections?

Within the penis are two long tubes of spongy tissue that run the length of the penis. These tubes are called the corpus cavernosa. They are highly vascularized, which means that they’re full of blood vessels. A taut membrane surrounds the spongy tissue within each corpora cavernosa, kind of like a spongy hot dog.

When the penis is stimulated or a guy gets turned on, the parasympathetic branch of the autonomic nervous system sends signals to the artery walls in the penis. These signals kick off a process that relaxes the smooth muscles in the walls of the arteries, increasing their diameter. This process does not happen in the veins. As a result, more blood flows into the penis, and the amount flowing out remains unchanged. This leads to a net increase of blood in the penis. The blood fills up the spongy tissue of the corpus cavernosum, and pushes against the taut outer membrane. As pressure increases, an erection begins to happen via hydraulic pressure. The increasing pressure also forces shut the veins, further reducing blood flow out of the penis. This enhances the erection process.

Why Things Might Go Floppy

Anything that interferes with sexual arousal and/or the physiological process that causes erections can be a boner-killer.

Many men, especially older men with cardiovascular problems, have difficulties with erections, or erectile dysfunction. This is largely a plumbing issue. The physiological process required for erections stops working properly. In other words, not enough blood gets into and stays in the penis. For these men, erectile dysfunction drugs such as Viagra and Cialis can be helpful, as they amplify the erection process. But sexual arousal is still required. That’s why a guy can take a pill but not get an erection until he and his partner hit the sheets. Sexual arousal is needed to kick off the physiological erection process.

Large quantities of alcohol, some recreational drugs, and many medications can also negatively impact the physiological process necessary for erections. However, when you hear of young guys struggling with erection difficulties, the culprit is almost always anxiety.

Anxiety is an emotional and physical response to real or perceived threat. The threat can be physical of psychological. In the context of sex and sexual performance, it’s psychological.

Here is a common example of the chain of anxious thoughts that some guys have when it comes to erections and sex:

“What if I can’t get/keep it up?”

“If I can’t get/keep it up, I won’t be able to have penetrative sex.”

“I need to be able to have penetrative sex for this experience to be good.”

“If I can’t have penetrative sex, my partner will be disappointed.”

“My partner will judge me.”

“I’m a failure as a sex partner.”

“I’m a failure as a man.”

“My partner will leave me or seek sex elsewhere.”

You can see how this chain of thoughts is based on perceived threat to the guy’s sense of being a good sex partner, his masculinity, and his ability to keep a partner. It’s highly anxiety provoking.

As anxiety increases, it interferes with erections in two ways.

First, anxiety is a distraction from what is sexually arousing. When a guy gets caught up in anxious thoughts about performance, all his mental resources get chewed up managing his fearful thoughts. This means that he stops focusing on the sensory and emotional experiences that heighten and maintain sexual arousal. For example, he may stop noticing the chemistry between him and his partner, the sensation of being physically stimulated, how visually appealing he finds his partner, and the sounds and smells that go along with sex. In other words, he becomes trapped in his head and loses touch with the sexual experience that he’s trying to enjoy.

Second, anxiety interferes with activation of the parasympathetic branch of the autonomic nervous system, which is required for the physiological erection process to happen. As the sympathetic branch of the autonomic nervous system becomes active in response to psychological threat, parasympathetic activity drops. And then so do erections.

The relationship between anxiety and erections is particularly cruel. Unlike other types of anxiety, there is a direct physiological impact that makes it difficult for a guy to do what it is that he wants (i.e., have penetrative sex). A person can be anxious about flying and still fly, about public speaking and still get up in front of an audience and speak, and about an exam and still write the exam. The same isn’t true about anxiety and erections. Having said that, there are many ways to have an awesome sexual experience that don’t require an erection.

The good news is that erection difficulties due to anxiety are not permanent. Some guys manage to get over it themselves, usually with the help of understanding partners. Others may need to seek the help of a psychologist or therapist. The same tools that are helpful in managing non-sexual anxiety work for performance anxiety. It’s simply a matter of learning them and putting them into action. Once that happens, it’s back to having great, worry-free sex.